hello all this is dr alsup and in this video we will be discussing the lumbar plexus and i know
the term plexus may raise some of our blood pressure a little but we will focus on the
basics here with an emphasis on where we can locate these name branches particularly
when we're talking about within the abdomen and then we will focus in a bit more on three
specific branches as the others will be discussed in more detail during the musculoskeletal content
so let's start with what makes up the lumbar plexus but before i get into that
i want you to think back to other plexuses we have discussed what were they composed of
so recall that the majority of the nervous plexuses that we have discussed so far
have been composed of almost exclusively autonomic fibers
the lumbar plexus and the sacral plexus which we'll talk about in upcoming videos are unique
in terms of what we've discussed so far they're not necessarily unique in terms of the overall
scheme of the nervous system but these are different in the fact that they are predominantly
somatic nervous plexuses so this means that the majority of the fibers that
are going to make up the lumbar plexus are either somatic afferent or efferent fibers
so they're innervating skeletal muscle they're innovating skin and other more somatic structures
these somatic fibers are derived from the ventral primary rami or the vprs
of spinal nerves L1 through L4 thus the name lumbar plexus so the l recall is the means lumbar
so those fibers from the vprs of L1 through L4 will braid they'll network and then they'll
coalesce into name branches which may have fibers from multiple spinal cord levels so
those branches that we'll talk about many of them are say from L2 and L3 or from L1 and L2 so they
have fibers from multiple spinal cord levels now when we're trying to identify those name branches
the psoas major muscle which i am outlining right here is going to be a major player an
important landmark in terms of identifying these so as major will actually share a common tendon
with the iliacus muscle right here and they will attach to the proximal femur and so these muscles
are often referred to together as the iliopsoas muscle and that's going to be an important and
powerful flexor of the hip joint but for today we're going to focus on the psoas major muscle
and its role as an important landmark for differentiating the branches of the lumbar plexus
in the abdomen there are six main branches of the lumbar plexus so starting superiorly
and making our way inferiorly so these will be the most superior of those branches
and these would be the most inferior the first two you're going to have are the iliohypogastric
and the ilioanguinal and you can actually see on this particular particular individual that
these nerves are coming off of a common trunk as they these are actually both derived from L1
and we'll talk about that in a bit more detail in a moment but if you don't have them coming
off the uh common trunk generally you'll have the iliohypogastric being the more superior one
with iloinguinal a little bit more inferiorly placed i hope you recall that the ilioinguinal
nerve is going to traverse the inguinal canal and so we'll come back to that in a moment as well
next you'll have the genitofemoral nerve which i think is the easiest to identify within the lumbar
plexus as this particular nerve will actually pierce through the belly of the genitofemoral
or of the psoas major muscle and you can see it piercing through and then kind of running along
the superficial border of the psoas major so that's something you'll see quite often
which muscle is going to pierce the psoas major muscle and it is the answer is genitofemoral
at around mid belly of the psoas major the lateral femoral cutaneous nerve
is going to be located kind of moving laterally i always think of it as heading towards the
anterior superior iliac spine which would be just around this general area maybe a little bit higher
up there and it's kind of crossing over the iliacus muscle as you can see here
the last two nerves are also the largest branches of the lumbar plexus and these are the obturator
nerve which isn't as easily identif identifiable on this particular image but it is going to be
kind of deep to the artery and vein right here and it will be more inferior medial
so it'd be kind of right around this region here whereas the femoral nerve which is the
largest branch of the lumbar plexus is going to be located on the inferior lateral border and
you can see that one here you don't have any arteries or veins blocking its view
so both of these nerves both the obturator and the femoral nerve are hugely important in terms
of musculoskeletal anatomy in terms of innervating large portions of the thigh musculature and skin
so we'll definitely kind of put a pin on those and we'll come back to those in more detail later
so let's spend the last few minutes of our time here focusing a bit more on the
functions of these more superior branches of the lumbar plexus as they have bigger roles
either in the abdomen or the pelvis or both so the iliohypogastric nerve which you can see here
is going to be composed of fibers of L1 and only fibers of L1 so not one of those typical plexus
nerves which will have fiber contributions from multiple levels this is also true of
the ilioinguinal nerve so both are derived from just fibers from L1 and this is why we often see
these nerves coming off of a common trunk before branching and heading to their target organs
both iliohypogastric and ilioinguin- inguinal nerves will afferently serve
portions of the anterior lateral abdominal wall so you can see that here and here um
so they're sending signals back to the central nervous system regarding what
is happening to the skin in that region or in terms of proprioception of those muscles there
additionally they will both provide efferent innervation to those same muscles
in addition the ilioinguinal nerve will provide afferent innervation to the superior medial thigh
as well as the anterior perineum and portions of the external genitalia so skinned over the mons
pubis and the labia majus or the root of the penis and upper part of the scrotum recall when we're
talking about the ilioinguinal nerve that it's going to traverse the inguinal canal superficial
to the round ligament or the spermatic cord and it will actually exit the superficial inguinal ring
so dividing into those terminal sensory branches that'll be important in terms of providing a fair
and innervation to this region lastly let's talk a few more specifics regarding the genitofemoral
nerve this is more like a typical plexus branch with fibers from multiple spinal cord levels
so we're talking L1 and L2 as its name would suggest there are actually two major branches
of the genitofemoral nerve there's going to be a genital branch as well as a femoral branch
and the genital branch in terms of afferent innervation is going to overlap considerably
in terms of area that it will innervate with the ilioinguinal nerve so you can see here mons pubis
labium majus and scrotum that's very similar to what you have in terms of the ilioinguinal nerve
so considerable overlap in that region the femoral branch of the genito femoral
is closely related as well but it's going to be a bit more in terms of the anterior medial
thigh whereas ilioinguinal is going to be a bit more superior
in terms of efferent innervation its genital branch is going to innervate the cremaster muscle
we haven't actually talked much about the cremaster muscle yet but it's located as
a very thin layer of muscle in the inguinal canal and continues surrounding the spermatic
cord or round ligament of the uterus even past the superficial inguinal ring it functions to pull the
round ligament or spermatic cord kind of towards the superficial inguinal ring when it contracts
with its most noticeable function of kind of pulling the testis towards the ring as
well so that's often when you see the function or the action that's often what you will see
all right excellent here is your summary slide again focus on how
you will locate these branches when you're looking
at the lumbar plexus in the abdomen with that special consideration of the psoas major muscle
and get down into the additional details of just these three nerves here in terms of the lumbar
plexus because the other nerves other three nerves we'll discuss in more detail later
on in the curriculum thank you for your time and attention here and have a great rest of your day